Still need another niche to help protect your business from competition, both local and overseas? If your company’s skill set is large, then maybe you should think small, as in very tiny components.
Micro components are not new in the world of manufacturing, but interest in microtechnology is growing. This was evident from the many exhibitors at the PDx/Amerimold trade show in May touting their micromolding capabilities. The evolution of computers, cell phones, and other gadgets, with their need for smaller plastic parts, has opened that world to injection molders and moldmakers.
An LED mold is cut on a Makino ultraprecision vertical machining center.
Micro- and even nano-sized components are taking center stage in manufacturing, but there’s a huge difference between the two. As Mark Kinder, president of Plastic Design Corp. (PDC) in Scottsdale, AZ, noted, “With nano you’re looking at things you can’t see except with a high-powered electron microscope, but micro parts you can see and measure.” Kinder, with Makino’s John Bradford, presented a session on “Machining for Micro Molds” during a seminar at Makino’s technical facility in Mason, OH, opened to customers and potential customers who, like MPW, were in town to attend the PDx/Amerimold trade show.
PDC has four micromolding machines—three Sumitomos and one Fanuc Roboshot—with clamp tonnage of 6, 7, and 18 for implantable medical devices. In addition, PDC uses a 100-ton Roboshot for molding microfluidic test plates. These plates are used in diagnostics laboratory testing, and while the plates are about 3 by 5 inches, each plate has many micro features cut into it (Kinder calls this “micro on macro”) that demand exacting molding performance in PDC’s Class 8 cleanroom. “Any bio burden on the plate itself can really muck up a test,” Kinder said, noting that during the H1N1 virus outbreak a year ago, PDC “went nuts” making enough plates to meet the demand for patient testing.
Forget the data sheet
One downside to molding micro parts is the “mechanical properties go to hell in a handbasket,” said Kinder. “Below 0.020-inch wall section, you lose tensile strength. Heat transfer is a problem, too.”
He explained that because you have so few molecular chains of plastic going into the mold, the plastic behaves differently from when you have a lot of plastic going into the mold. Additionally, when molding micro parts, “You’re slipping the skin and pushing it through the mold. Below ½ mm [500 µm], you can’t keep the core melt going.” As a result of these challenges, PDC always characterizes the plastic before it builds a mold.
If molding is different, so is building a mold for these micro parts. Kinder presented a micro mold construction case history at the Makino seminar. PDC has four Makino machines, two V22s, an Edge 2 Sinker, and a small-wire EDM (U32j) that runs wire in 0.002-, 0.004-, and 0.008-inch diameter.
John Bradford, micromachining R&D manager for Makino, said, “When you get to a feature size below 8 µm, you need ultraprecision machine tools.” The key to machining molds for micromolding, he said, is to control the tip of the cutting tool as it interfaces with the workpiece. “We’re using tools as small as 0.010 µm on the same spindle, and micro-drilling holes below 0.100 µm using multiple tools in a submicron cutting,” he explained.
“We’re looking at how to reduce tooling costs on these micro molds. Machining parts you can’t see with the naked eye has its challenges,” said Bradford. “These are high-cost, high-value components—how to mold these to get the cost out is a challenge as well. It’s tough when you can’t physically see the tools.”
The part PDC displayed for the case study is molded in PEEK for an implantable micro medical device called a Bone Anchor, which weighs 7 mg and is 2 mm long. “PEEK is favored for use in long-term implantable devices in bone because it approximates the modulus of bone,” Kinder explained.
However, using PEEK means that the part has to be processed at a high temperature—from 385-400°F for the mold, with the screw and barrel at 740-770°F. Because of outgassing, good venting in the mold is a must, Kinder noted. “The material also flashes easily but we needed—and were able to get—nice, sharp edges by laminating the mold,” Kinder said.
While PDC began as an R&D center, it evolved into this micromolding niche for a couple of reasons. “The barrier to play in this sandbox is pretty high. Six years ago we entered it because we felt it was an arena that China wouldn’t be quick to develop,” recalled Kinder. “People are just finding out what ‘micro’ can do.” —Clare Goldsberry